The Immune System: Reading Activity!
Felt sick recently? You might have been under attack! Many
illnesses are caused by living things inside our bodies, called
pathogens, that are harming our cells. Fortunately, your body can
fight back! When pathogens attack, our body responds with the
immune system. The immune system is responsible for defending
the body against disease.
Fighting disease-causing pathogens is serious work, so your immune
system is actually made up of three lines of defense. Let’s call the
first line of defense the barriers. In the first line of defense, the
skin, breathing passages, and mouth and stomach act as barriers.
They trap and kill most pathogens we come into contact with.
Let’s start with your skin. Destructive chemicals in skin oils and
sweat destroy many pathogens that land on your skin. The
pathogens that remain can’t make it through the layers of dead cells
that protect the living skin cells underneath. Pathogens can get
through the skin if it is cut, but scabs form so quickly that pathogens
don’t have much time to get in this way.
Pathogens can enter your body when you inhale, but the breathing
passages of your respiratory system – nose, pharynx, trachea and
bronchi – are armed with mucus and cilia. The sticky mucus traps
pathogens, and the cilia sweeps it away to be swallowed and
destroyed in your stomach. In addition, sneezing and coughing force
pathogens out of your body.
Finally, your mouth and stomach of your digestive system can
destroy many pathogens you swallow – for example, in infected
food. Saliva in your mouth contains chemicals that kill pathogens. If
the pathogens make it down to your stomach, they will be
destroyed by stomach acid.
If pathogens get into your body and begin to damage your cells,
your body’s second line of defense kicks in. The second line of
defense is called the inflammatory response. In the inflammatory
response, blood vessels widen to send extra blood to nearby
tissues.
Your blood isn’t just made up of red blood cells. Your blood also has
disease-fighting white blood cells. In the inflammatory response,
when extra blood goes to tissue affected by a pathogen, a type of
white blood cell called a phagocyte (fadge-o-sight) attacks
pathogens. The phagocyte attacks pathogens by engulfing them –
by swallowing them whole and breaking them down.
If pathogens harm cells enough to cause fever, your third line of
defense steps up. The third line of defense is called the immune
response. The cells of the immune response can tell the difference
between different kinds of pathogens, and react to each kind of
pathogen with a targeted response.
Remember, white blood cells are disease fighters, and two types of
white blood cells play big roles in your immune response. The first
are called T cells. The job of a T cell is to recognize what specific
kind of pathogen the body is dealing with. There are tens of millions
of T cells in your body, looking for different types of pathogens.
The T cells then go find the other white blood cell of the immune
response, B cells. B cells are able to make substances called
antibodies that target specific pathogens. These antibodies attach
themselves to pathogens, making it difficult for the pathogens to
attach themselves to healthy cells. Antibodies also cause pathogens
to clump together, which makes them easy targets for phagocytes
to come along and eat up the pathogens!
This is a phagocyte of your
second line of defense
eating a bacterium.
You’re done with the reading!
Nice work!
Move on to Level B!